CHICAGO (Reuters) - Genome pioneer J. Craig Venter is teaming up with a unit of United Therapeutics Corp to develop pig lungs that have been genetically altered to be compatible with humans, a feat that, if successful, could address the urgent need for transplant organs for people with end-stage lung disease.

Venter's privately held company Synthetic Genomics Inc on Tuesday said it has entered a multiyear deal with United Therapeutics' Lung Biotechnology Inc to develop the so-called humanized pig organs.

The venture is intended to advance United Therapeutics' efforts to develop replacement organs grown in genetically altered pigs. According to the companies, about 400,000 people in the United States die each year from various forms of lung disease, and only 2,000 people are saved with a lung transplant.

Prior efforts to use animal organs in people in need of a transplant, known as xenotransplantation, have failed because of differences in the genome that caused organ rejection and blood clots.

Silver Spring, Maryland-based United Therapeutics, said in a statement.

Humans, pigs and most other mammals share about 90 percent of the same genes. What Venter's team will do is to determine which aspects of the pig genome need to be altered to make porcine lungs compatible with humans, avoiding the rejection response that occurs even in human-to-human transplants.

"We're going to start with generating a brand new super-accurate sequence of the pig genome, and then go through in detail and compare it to the human genome," Venter, the founder and chief executive of Synthetic Genomics Inc, said in a telephone interview.

"The goal is to go in and edit, and where necessary, rewrite using our synthetic genomic tools, the pig genes that seem to be associated with immune responses," said Venter, who is best known for his role in mapping the human genome over a decade ago and who created synthetic life in 2010.

"We want to get it so there is no acute or chronic rejection," he said.

Venter's team is tasked with editing and rewriting the pig genome and providing the United Therapeutics group with a series of altered cells. United Therapeutics will take those cells and transplant them into pig eggs, generating embryos that develop and are born with humanized lungs.

If all goes well, Venter thinks his team will be able to deliver the cells in a few years. Testing the humanized organs in clinical trials to ensure they are safe in people will take many more years.

Lungs are the hardest organ to transplant because they are so delicate in structure, Venter says. So, if the team succeeds in developing humanized pig lungs, hearts and kidneys from these animals may also prove to be suitable for human transplantation.

As part of the agreement, Lung Biotechnology will take a $50 million stake in La Jolla, California-based Synthetic Genomics, which also will receive royalties and milestone incentives from the development and commercialization of the organs.

Venter admits that just five years ago, the venture would have sounded like science fiction. But several research teams are working on the use of genetically altered pig body parts to help improve the supply of transplant organs.

Last week, researchers at the National Heart, Lung, and Blood Institute reported at the American Association for Thoracic Surgery meeting in Toronto that they grafted a genetically altered pig heart into the abdomen of a baboon and kept it functioning, aided by the baboon's natural heart, for more than a year.